Amnesty International is urging Southeast Asian nations to avoid a repeat of the refugee-boat crisis that left thousands stranded at sea earlier this year, saying in a new report that human traffickers kept asylum-seekers in “hellish” conditions, beat them severely and even killed them if families failed to pay ransoms.

The report released Wednesday is based on interviews with more than 100 Rohingya Muslim refugees who reached Indonesia through perilous boat journeys.

“The daily physical abuse faced by Rohingya who were trapped on boats in the Bay of Bengal and Andaman Sea is almost too horrific to put into words … Even children were not spared these abuses,” said Anna Shea, a refugee researcher at Amnesty.

Tens of thousands of Rohingya have fled Myanmar by boat to escape persecution by the country’s Buddhist majority. Their plight became an international crisis in May when thousands of Rohingya and Bangladeshis were found packed in rickety boats with little food or water, abandoned by their smugglers. Some were turned away by the governments of Thailand and Malaysia, while some managed to make it to shore in Indonesia.

“The shocking truth is that those we spoke to are the ‘lucky’ ones who made it to shore — countless others perished at sea or were trafficked into forced labor situations,” said Shea.

The mostly ethnic Rohingya are Muslims who have lived in Myanmar’s western state of Arakan (Rakhine) as a minority for generations but are not recognized by the government as citizens. Instead, they are branded as foreigners with no rights, and face constant discrimination from the government as well as Buddhist nationalists.

State sponsored violence by Buddhist has left more than 200 dead, mostly Rohingya. Another 140,000 were driven from their homes by Buddhist mobs. Displaced Rohingya who have not fled the country live in squalid camps in search of better lives.

With the monsoon ending and a new “sailing season” already underway, thousands more Rohingya could be taking to boats, Amnesty said, as it urged regional governments to urgently step up their response.